Ballonet for a balloon

ABSTRACT

A self-stabilizing bladder or ballonet is provided within an envelope of a balloon. The bladder includes a spheroid body comprising an equator, a top pole, a bottom pole, and an axis crossing through the top pole and the bottom pole. The distance between two poles may be less than the equatorial distance. The bladder is sized and shaped for insertion into an envelope of a balloon and is inflatable to provide altitude control for the balloon.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Computing devices such as personal computers, laptop computers, tabletcomputers, cellular phones, and countless types of Internet-capabledevices are increasingly prevalent in numerous aspects of modern life.As such, the demand for data connectivity via the Internet, cellulardata networks, and other such networks, is growing. However, there aremany areas of the world where data connectivity is still unavailable, orif available, is unreliable and/or costly. Accordingly, additionalnetwork infrastructure is desirable. A high-altitude balloon network canprovide communication with ground-based station(s) using RFcommunications.

SUMMARY

A bladder or ballonet is provided within an envelope of a balloon. Thebladder has a spheroid shape and is foldable for insertion into theballoon prior to performing a final seam on the balloon. The bladder'sshape may be the same as or similar to the curvature of the interiorsurface of the balloon. As the bladder is filled with liquid or gas, theshape of the bladder cooperates with the shape of the balloon such thatthe bladder does not require any additional stabilizing elements.

In one aspect, an example inflatable bladder includes a spheroid bodycomprising an equator, a top pole, a bottom pole, and an axis crossingthrough the top pole and the bottom pole generally perpendicular to theequator. A distance around the equator is greater than a distance aroundthe axis. The inflatable bladder is sized and shaped for insertion intoan envelope of a balloon.

In another aspect, an example variable buoyancy system involves aballoon comprising an envelope. The envelope comprises an interior thatcontains a liquid or gas. A ballonet is within the envelope interior.The ballonet has a spheroid body comprising an equator, a top pole, abottom pole, and an axis crossing through the top pole and the bottompole generally perpendicular to the equator. The distance around theequator is greater than the distance around the axis.

In a further aspect, an example method involves providing a plurality ofsheets, seaming two or more of the plurality of sheets together to forma spheroid-shaped ballonet, inserting the ballonet into a balloon, andsealing the ballonet at a base of the balloon.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram illustrating a balloon network, accordingto an example embodiment.

FIG. 2 is a diagram illustrating a balloon-network control system,according to an example embodiment.

FIG. 3 is a simplified diagram illustrating a high-altitude balloon,according to an example embodiment.

FIG. 4 is a simplified diagram illustrating a balloon network thatincludes super-nodes and sub-nodes, according to an example embodiment.

FIG. 5 is a simplified diagram illustrating a ballonet for use inside ofa high-altitude balloon, according to an example embodiment.

FIG. 6 is a flow chart of a method, according to an example embodiment.

FIG. 7 is a simplified diagram illustrating sheets to manufacture aballonet, according to an example embodiment.

DETAILED DESCRIPTION

Example methods and systems are described herein. Any example embodimentor feature described herein is not necessarily to be construed aspreferred or advantageous over other embodiments or features. Theexample embodiments described herein are not meant to be limiting. Itwill be readily understood that certain aspects of the disclosed systemsand methods can be arranged and combined in a wide variety of differentconfigurations, all of which are contemplated herein.

Furthermore, the particular arrangements shown in the Figures should notbe viewed as limiting. It should be understood that other embodimentsmay include more or less of each element shown in a given Figure.Further, some of the illustrated elements may be combined or omitted.Yet further, an example embodiment may include elements that are notillustrated in the Figures.

1. OVERVIEW

Example embodiments disclosed herein generally relate to an inflatablebladder for use with a high-altitude balloon deployed in thestratosphere. In order that the balloons can provide a reliable meshnetwork in the stratosphere, inflatable bladders may be installed withinthe balloons for altitude control. By controlling the balloon'sbuoyancy, balloons can be driven up and down in the atmosphere or heldat a constant altitude for long duration flights. Altitude control thusenables some form of navigation for the balloon.

An inflatable bladder, or ballonet, may be inflated with a liquid and/orgas to add mass to a constant-volume (e.g., superpressure) balloon,causing the balloon to descend; and conversely, deflating the bladdercauses the balloon to rise. In some example embodiments, an inflatablebladder may comprise an oblate or a rounded shape with generallyflattened poles that is manufactured from two or more sheets of materialseamed together. Advantageously, the shape of the bladder readily fitsto the curvature of a balloon that is also oblate in shape, and as thebladder is filled with either liquid or gas the bladder wants to rightitself, preventing the bladder from filling to one side during thefilling process. This in turn prevents destabilizing the balloon.

Such an inflatable bladder is easy and inexpensive to fabricate and isscalable in size. For example, using wider sheets or attaching more thantwo sheets together may provide for a larger diameter bladder.Additionally, the shape of the inflatable bladder allows for compactfolding of the bladder for insertion into a balloon, providing forreduced manipulation or handling of the balloon.

2. EXAMPLE BALLOON NETWORKS

In an example balloon network, balloons may communicate with one anotherusing free-space optical communications. For instance, the balloons maybe configured for optical communications using ultra-bright LEDs (whichare also referred to as “high-power” or “high-output” LEDs). In someinstances, lasers could be used instead of or in addition to LEDs,although regulations for laser communications may restrict laser usage.In addition, the balloons may communicate with ground-based station(s)using radio-frequency (RF) communications.

In some embodiments, a high-altitude-balloon network may be homogenous.That is, the balloons in a high-altitude-balloon network could besubstantially similar to each other in one or more ways. Morespecifically, in a homogenous high-altitude-balloon network, eachballoon is configured to communicate with nearby balloons via free-spaceoptical links. Further, some or all of the balloons in such a network,may also be configured to communicate with ground-based station(s) usingRF communications. (Note that in some embodiments, the balloons may behomogenous in so far as each balloon is configured for free-spaceoptical communication with other balloons, but heterogeneous with regardto RF communications with ground-based stations.)

In other embodiments, a high-altitude-balloon network may beheterogeneous, and thus may include two or more different types ofballoons. For example, some balloons may be configured as super-nodes,while other balloons may be configured as sub-nodes. Some balloons maybe configured to function as both a super-node and a sub-node. Suchballoons may function as either a super-node or a sub-node at aparticular time, or, alternatively, act as both simultaneously dependingon the context. For instance, an example balloon could aggregate searchrequests of a first type to transmit to a ground-based station. Theexample balloon could also send search requests of a second type toanother balloon, which could act as a super-node in that context.

In such a configuration, the super-node balloons may be configured tocommunicate with nearby super-node balloons via free-space opticallinks. However, the sub-node balloons may not be configured forfree-space optical communication, and may instead be configured for someother type of communication, such as RF communications. In that case, asuper-node may be further configured to communicate with sub-nodes usingRF communications. Thus, the sub-nodes may relay communications betweenthe super-nodes and one or more ground-based stations using RFcommunications. In this way, the super-nodes may collectively functionas backhaul for the balloon network, while the sub-nodes function torelay communications from the super-nodes to ground-based stations.Other differences could be present between balloons in a heterogeneousballoon network.

FIG. 1 is a simplified diagram illustrating a balloon network 100,according to an example embodiment. As shown, balloon network 100includes balloons 102A to 102F, which are configured to communicate withone another via free-space optical links 104. Balloons 102A to 102Fcould additionally or alternatively be configured to communicate withone another via RF links 114. Balloons 102A to 102F may collectivelyfunction as a mesh network for packet-data communications. Further,balloons 102A to 102F may be configured for RF communications withground-based stations 106 and 112 via RF links 108. In another exampleembodiment, balloons 102A to 102F could be configured to communicate viaoptical link 110 with ground-based station 112.

In an example embodiment, balloons 102A to 102F are high-altitudeballoons, which are deployed in the stratosphere. At moderate latitudes,the stratosphere includes altitudes between approximately 10 kilometers(km) and 50 km altitude above the surface. At the poles, thestratosphere starts at an altitude of approximately 8 km. In an exampleembodiment, high-altitude balloons may be generally configured tooperate in an altitude range within the stratosphere that has lowerwinds (e.g., between 5 and 20 miles per hour (mph)).

More specifically, in a high-altitude-balloon network, balloons 102A to102F may generally be configured to operate at altitudes between 17 kmand 25 km (although other altitudes are possible). This altitude rangemay be advantageous for several reasons. In particular, this layer ofthe stratosphere generally has mild wind and turbulence (e.g., windsbetween 5 and 20 miles per hour (mph)). Further, while the winds between17 km and 25 km may vary with latitude and by season, the variations canbe modelled in a reasonably accurate manner. Additionally, altitudesabove 17 km are typically above the maximum flight level designated forcommercial air traffic. Therefore, interference with commercial flightsis not a concern when balloons are deployed between 17 km and 25 km.

To transmit data to another balloon, a given balloon 102A to 102F may beconfigured to transmit an optical signal via an optical link 104. In anexample embodiment, a given balloon 102A to 102F may use one or morehigh-power light-emitting diodes (LEDs) to transmit an optical signal.Alternatively, some or all of balloons 102A to 102F may include lasersystems for free-space optical communications over optical links 104.Other types of free-space optical communication are possible. Further,in order to receive an optical signal from another balloon via anoptical link 104, a given balloon 102A to 102F may include one or moreoptical receivers. Additional details of example balloons are discussedin greater detail below, with reference to FIG. 3.

In a further aspect, balloons 102A to 102F may utilize one or more ofvarious different RF air-interface protocols for communicationground-based stations 106 and 112 via RF links 108. For instance, someor all of balloons 102A to 102F may be configured to communicate withground-based stations 106 and 112 using protocols described in IEEE802.11 (including any of the IEEE 802.11 revisions), various cellularprotocols such as GSM, CDMA, UMTS, EV-DO, WiMAX, and/or LTE, and/or oneor more propriety protocols developed for balloon-to-ground RFcommunication, among other possibilities.

In a further aspect, there may scenarios where RF links 108 do notprovide a desired link capacity for balloon-to-ground communications.For instance, increased capacity may be desirable to provide backhaullinks from a ground-based gateway, and in other scenarios as well.Accordingly, an example network may also include downlink balloons,which could provide a high-capacity air-ground link.

For example, in balloon network 100, balloon 102F could be configured asa downlink balloon. Like other balloons in an example network, adownlink balloon 102F may be operable for optical communication withother balloons via optical links 104. However, downlink balloon 102F mayalso be configured for free-space optical communication with aground-based station 112 via an optical link 110. Optical link 110 maytherefore serve as a high-capacity link (as compared to an RF link 108)between the balloon network 100 and a ground-based station 112.

Note that in some implementations, a downlink balloon 102F mayadditionally be operable for RF communication with ground-based stations106. In other cases, a downlink balloon 102F may only use an opticallink for balloon-to-ground communications. Further, while thearrangement shown in FIG. 1 includes just one downlink balloon 102F, anexample balloon network can also include multiple downlink balloons. Onthe other hand, a balloon network can also be implemented without anydownlink balloons.

In other implementations, a downlink balloon may be equipped with aspecialized, high-bandwidth RF communication system forballoon-to-ground communications, instead of, or in addition to, afree-space optical communication system. The high-bandwidth RFcommunication system may take the form of an ultra-wideband system,which provides an RF link with substantially the same capacity as theoptical links 104. Other forms are also possible.

Balloons could be configured to establish a communication link withspace-based satellites in addition to, or as an alternative to, aground-based communication link.

Ground-based stations, such as ground-based stations 106 and/or 112, maytake various forms. Generally, a ground-based station may includecomponents such as transceivers, transmitters, and/or receivers forcommunication via RF links and/or optical links with a balloon network.Further, a ground-based station may use various air-interface protocolsin order communicate with a balloon 102A to 102F over an RF link 108. Assuch, ground-based stations 106 and 112 may be configured as an accesspoint with which various devices can connect to balloon network 100.Ground-based stations 106 and 112 may have other configurations and/orserve other purposes without departing from the scope of the invention.

Further, some ground-based stations, such as ground-based stations 106and 112, may be configured as gateways between balloon network 100 andone or more other networks. Such ground-based stations 106 and 112 maythus serve as an interface between the balloon network and the Internet,a cellular service provider's network, and/or other types of networks.Variations on this configuration and other configurations ofground-based stations 106 and 112 are also possible.

2a) Mesh Network Functionality

As noted, balloons 102A to 102F may collectively function as a meshnetwork. More specifically, since balloons 102A to 102F may communicatewith one another using free-space optical links, the balloons maycollectively function as a free-space optical mesh network.

In a mesh-network configuration, each balloon 102A to 102F may functionas a node of the mesh network, which is operable to receive datadirected to it and to route data to other balloons. As such, data may berouted from a source balloon to a destination balloon by determining anappropriate sequence of optical links between the source balloon and thedestination balloon. These optical links may be collectively referred toas a “lightpath” for the connection between the source and destinationballoons. Further, each of the optical links may be referred to as a“hop” on the lightpath.

To operate as a mesh network, balloons 102A to 102F may employ variousrouting techniques and self-healing algorithms. In some embodiments, aballoon network 100 may employ adaptive or dynamic routing, where alightpath between a source and destination balloon is determined andset-up when the connection is needed, and released at a later time.Further, when adaptive routing is used, the lightpath may be determineddynamically depending upon the current state, past state, and/orpredicted state of the balloon network.

In addition, the network topology may change as the balloons 102A to102F move relative to one another and/or relative to the ground.Accordingly, an example balloon network 100 may apply a mesh protocol toupdate the state of the network as the topology of the network changes.For example, to address the mobility of the balloons 102A to 102F,balloon network 100 may employ and/or adapt various techniques that areemployed in mobile ad hoc networks (MANETs). Other examples are possibleas well.

In some implementations, a balloon network 100 may be configured as atransparent mesh network. More specifically, in a transparent balloonnetwork, the balloons may include components for physical switching thatis entirely optical, without any electrical involved in physical routingof optical signals. Thus, in a transparent configuration with opticalswitching, signals travel through a multi-hop lightpath that is entirelyoptical.

In other implementations, the balloon network 100 may implement afree-space optical mesh network that is opaque. In an opaqueconfiguration, some or all balloons 102A to 102F may implementoptical-electrical-optical (OEO) switching. For example, some or allballoons may include optical cross-connects (OXCs) for OEO conversion ofoptical signals. Other opaque configurations are also possible.Additionally, network configurations are possible that include routingpaths with both transparent and opaque sections.

In a further aspect, balloons in an example balloon network 100 mayimplement wavelength division multiplexing (WDM), which may help toincrease link capacity. When WDM is implemented with transparentswitching, physical lightpaths through the balloon network may besubject to the “wavelength continuity constraint.” More specifically,because the switching in a transparent network is entirely optical, itmay be necessary to assign the same wavelength for all optical links ona given lightpath.

An opaque configuration, on the other hand, may avoid the wavelengthcontinuity constraint. In particular, balloons in an opaque balloonnetwork may include the OEO switching systems operable for wavelengthconversion. As a result, balloons can convert the wavelength of anoptical signal at each hop along a lightpath. Alternatively, opticalwavelength conversion could take place at only selected hops along thelightpath.

Further, various routing algorithms may be employed in an opaqueconfiguration. For example, to determine a primary lightpath and/or oneor more diverse backup lightpaths for a given connection, exampleballoons may apply or consider shortest-path routing techniques such asDijkstra's algorithm and k-shortest path, and/or edge and node-diverseor disjoint routing such as Suurballe's algorithm, among others.Additionally or alternatively, techniques for maintaining a particularQuality of Service (QoS) may be employed when determining a lightpath.Other techniques are also possible.

2b) Station-Keeping Functionality

In an example embodiment, a balloon network 100 may implementstation-keeping functions to help provide a desired network topology.For example, station-keeping may involve each balloon 102A to 102Fmaintaining and/or moving into a certain position relative to one ormore other balloons in the network (and possibly in a certain positionrelative to the ground). As part of this process, each balloon 102A to102F may implement station-keeping functions to determine its desiredpositioning within the desired topology, and if necessary, to determinehow to move to the desired position.

The desired topology may vary depending upon the particularimplementation. In some cases, balloons may implement station-keeping toprovide a substantially uniform topology. In such cases, a given balloon102A to 102F may implement station-keeping functions to position itselfat substantially the same distance (or within a certain range ofdistances) from adjacent balloons in the balloon network 100.

In other cases, a balloon network 100 may have a non-uniform topology.For instance, example embodiments may involve topologies where balloonsare distributed more or less densely in certain areas, for variousreasons. As an example, to help meet the higher bandwidth demands thatare typical in urban areas, balloons may be clustered more densely overurban areas. For similar reasons, the distribution of balloons may bedenser over land than over large bodies of water. Many other examples ofnon-uniform topologies are possible.

In a further aspect, the topology of an example balloon network may beadaptable. In particular, station-keeping functionality of exampleballoons may allow the balloons to adjust their respective positioningin accordance with a change in the desired topology of the network. Forexample, one or more balloons could move to new positions to increase ordecrease the density of balloons in a given area. Other examples arepossible.

In some embodiments, a balloon network 100 may employ an energy functionto determine if and/or how balloons should move to provide a desiredtopology. In particular, the state of a given balloon and the states ofsome or all nearby balloons may be input to an energy function. Theenergy function may apply the current states of the given balloon andthe nearby balloons to a desired network state (e.g., a statecorresponding to the desired topology). A vector indicating a desiredmovement of the given balloon may then be determined by determining thegradient of the energy function. The given balloon may then determineappropriate actions to take in order to effectuate the desired movement.For example, a balloon may determine an altitude adjustment oradjustments such that winds will move the balloon in the desired manner.

2c) Control of Balloons in a Balloon Network

In some embodiments, mesh networking and/or station-keeping functionsmay be centralized. For example, FIG. 2 is a diagram illustrating aballoon-network control system, according to an example embodiment. Inparticular, FIG. 2 shows a distributed control system, which includes acentral control system 200 and a number of regional control-systems 202Ato 202B. Such a control system may be configured to coordinate certainfunctionality for balloon network 204, and as such, may be configured tocontrol and/or coordinate certain functions for balloons 206A to 206I.

In the illustrated embodiment, central control system 200 may beconfigured to communicate with balloons 206A to 206I via number ofregional control systems 202A to 202C. These regional control systems202A to 202C may be configured to receive communications and/oraggregate data from balloons in the respective geographic areas thatthey cover, and to relay the communications and/or data to centralcontrol system 200. Further, regional control systems 202A to 202C maybe configured to route communications from central control system 200 tothe balloons in their respective geographic areas. For instance, asshown in FIG. 2, regional control system 202A may relay communicationsand/or data between balloons 206A to 206C and central control system200, regional control system 202B may relay communications and/or databetween balloons 206D to 206F and central control system 200, andregional control system 202C may relay communications and/or databetween balloons 206G to 206I and central control system 200.

In order to facilitate communications between the central control system200 and balloons 206A to 206I, certain balloons may be configured asdownlink balloons, which are operable to communicate with regionalcontrol systems 202A to 202C. Accordingly, each regional control system202A to 202C may be configured to communicate with the downlink balloonor balloons in the respective geographic area it covers. For example, inthe illustrated embodiment, balloons 206A, 206F, and 206I are configuredas downlink balloons. As such, regional control systems 202A to 202C mayrespectively communicate with balloons 206A, 206F, and 206I via opticallinks 206, 208, and 210, respectively.

In the illustrated configuration, where only some of balloons 206A to206I are configured as downlink balloons, the balloons 206A, 206F, and206I that are configured as downlink balloons may function to relaycommunications from central control system 200 to other balloons in theballoon network, such as balloons 206B to 206E, 206G, and 206H. However,it should be understood that it in some implementations, it is possiblethat all balloons may function as downlink balloons. Further, while FIG.2 shows multiple balloons configured as downlink balloons, it is alsopossible for a balloon network to include only one downlink balloon.

Note that a regional control system 202A to 202C may in fact just be aparticular type of ground-based station that is configured tocommunicate with downlink balloons (e.g. the ground-based station 112 ofFIG. 1). Thus, while not shown in FIG. 2, a control system may beimplemented in conjunction with other types of ground-based stations(e.g., access points, gateways, etc.).

In a centralized control arrangement, such as that shown in FIG. 2, thecentral control system 200 (and possibly regional control systems 202Ato 202C as well) may coordinate certain mesh-networking functions forballoon network 204. For example, balloons 206A to 206I may send thecentral control system 200 certain state information, which the centralcontrol system 200 may utilize to determine the state of balloon network204. The state information from a given balloon may include locationdata, optical-link information (e.g., the identity of other balloonswith which the balloon has established an optical link, the bandwidth ofthe link, wavelength usage and/or availability on a link, etc.), winddata collected by the balloon, and/or other types of information.Accordingly, the central control system 200 may aggregate stateinformation from some or all the balloons 206A to 206I in order todetermine an overall state of the network.

The overall state of the network may then be used to coordinate and/orfacilitate certain mesh-networking functions such as determininglightpaths for connections. For example, the central control system 200may determine a current topology based on the aggregate stateinformation from some or all the balloons 206A to 206I. The topology mayprovide a picture of the current optical links that are available in theballoon network and/or the wavelength availability on the links. Thistopology may then be sent to some or all of the balloons so that arouting technique may be employed to select appropriate lightpaths (andpossibly backup lightpaths) for communications through the balloonnetwork 204.

In a further aspect, the central control system 200 (and possiblyregional control systems 202A to 202C as well) may also coordinatecertain station-keeping functions for balloon network 204. For example,the central control system 200 may input state information that isreceived from balloons 206A to 206I to an energy function, which mayeffectively compare the current topology of the network to a desiredtopology, and provide a vector indicating a direction of movement (ifany) for each balloon, such that the balloons can move towards thedesired topology. Further, the central control system 200 may usealtitudinal wind data to determine respective altitude adjustments thatmay be initiated to achieve the movement towards the desired topology.The central control system 200 may provide and/or support otherstation-keeping functions as well.

FIG. 2 shows a distributed arrangement that provides centralizedcontrol, with regional control systems 202A to 202C coordinatingcommunications between a central control system 200 and a balloonnetwork 204. Such an arrangement may be useful to provide centralizedcontrol for a balloon network that covers a large geographic area. Insome embodiments, a distributed arrangement may even support a globalballoon network that provides coverage everywhere on earth. Adistributed-control arrangement may be useful in other scenarios aswell.

Further, it should be understood that other control-system arrangementsare possible. For instance, some implementations may involve acentralized control system with additional layers (e.g., sub-regionsystems within the regional control systems, and so on). Alternatively,control functions may be provided by a single, centralized, controlsystem, which communicates directly with one or more downlink balloons.

In some embodiments, control and coordination of a balloon network maybe shared between a ground-based control system and a balloon network tovarying degrees, depending upon the implementation. In fact, in someembodiments, there may be no ground-based control systems. In such anembodiment, all network control and coordination functions may beimplemented by the balloon network itself. For example, certain balloonsmay be configured to provide the same or similar functions as centralcontrol system 200 and/or regional control systems 202A to 202C. Otherexamples are also possible.

Furthermore, control and/or coordination of a balloon network may bede-centralized. For example, each balloon may relay state informationto, and receive state information from, some or all nearby balloons.Further, each balloon may relay state information that it receives froma nearby balloon to some or all nearby balloons. When all balloons doso, each balloon may be able to individually determine the state of thenetwork. Alternatively, certain balloons may be designated to aggregatestate information for a given portion of the network. These balloons maythen coordinate with one another to determine the overall state of thenetwork.

Further, in some aspects, control of a balloon network may be partiallyor entirely localized, such that it is not dependent on the overallstate of the network. For example, individual balloons may implementstation-keeping functions that only consider nearby balloons. Inparticular, each balloon may implement an energy function that takesinto account its own state and the states of nearby balloons. The energyfunction may be used to maintain and/or move to a desired position withrespect to the nearby balloons, without necessarily considering thedesired topology of the network as a whole. However, when each balloonimplements such an energy function for station-keeping, the balloonnetwork as a whole may maintain and/or move towards the desiredtopology.

As an example, each balloon A may receive distance information d₁ tod_(k) with respect to each of its k closest neighbors. Each balloon Amay treat the distance to each of the k balloons as a virtual springwith vector representing a force direction from the first nearestneighbor balloon i toward balloon A and with force magnitudeproportional to d_(i). The balloon A may sum each of the k vectors andthe summed vector is the vector of desired movement for balloon A.Balloon A may attempt to achieve the desired movement by controlling itsaltitude.

Alternatively, this process could assign the force magnitude of each ofthese virtual forces equal to d_(i)×d_(I), wherein d_(I) is proportionalto the distance to the second nearest neighbor balloon, for instance.

In another embodiment, a similar process could be carried out for eachof the k balloons and each balloon could transmit its planned movementvector to its local neighbors. Further rounds of refinement to eachballoon's planned movement vector can be made based on the correspondingplanned movement vectors of its neighbors. It will be evident to thoseskilled in the art that other algorithms could be implemented in aballoon network in an effort to maintain a set of balloon spacingsand/or a specific network capacity level over a given geographiclocation.

2d) Example Balloon Configuration

Various types of balloon systems may be incorporated in an exampleballoon network. As noted above, an example embodiment may utilizehigh-altitude balloons, which could typically operate in an altituderange between 17 km and 25 km. FIG. 3 shows a high-altitude balloon 300,according to an example embodiment. As shown, the balloon 300 includesan envelope 302, a skirt 304, a payload 306, and a cut-down system 308,which is attached between the balloon 302 and payload 304.

The envelope 302 and skirt 304 may take various forms, which may becurrently well-known or yet to be developed. For instance, the envelope302 and/or skirt 304 may be made of a highly-flexible latex material ormay be made of a rubber material such as chloroprene. In one exampleembodiment, the envelope and/or skirt could be made of metalized Mylaror BoPet. Other materials are also possible. Further, the shape and sizeof the envelope 302 and skirt 304 may vary depending upon the particularimplementation. Additionally, the envelope 302 may be filled withvarious different types of gases, such as helium and/or hydrogen. Othertypes of gases are possible as well.

The payload 306 of balloon 300 may include a processor 312 and on-boarddata storage, such as memory 314. The memory 314 may take the form of orinclude a non-transitory computer-readable medium. The non-transitorycomputer-readable medium may have instructions stored thereon, which canbe accessed and executed by the processor 312 in order to carry out theballoon functions described herein.

The payload 306 of balloon 300 may also include various other types ofequipment and systems to provide a number of different functions. Forexample, payload 306 may include optical communication system 316, whichmay transmit optical signals via an ultra-bright LED system 320, andwhich may receive optical signals via an optical-communication receiver322 (e.g., a photodiode receiver system). Further, payload 306 mayinclude an RF communication system 318, which may transmit and/orreceive RF communications via an antenna system 340.

The payload 306 may also include a power supply 326 to supply power tothe various components of balloon 300. The power supply 326 couldinclude a rechargeable battery. In other embodiments, the power supply326 may additionally or alternatively represent other means known in theart for producing power. In addition, the balloon 300 may include asolar power generation system 327. The solar power generation system 327may include solar panels and could be used to generate power thatcharges and/or is distributed by power supply 326.

Further, payload 306 may include various types of other systems andsensors 328. For example, payload 306 may include one or more videoand/or still cameras, a GPS system, various motion sensors (e.g.,accelerometers, magnetometers, gyroscopes, and/or compasses), and/orvarious sensors for capturing environmental data. Further, some or allof the components within payload 306 may be implemented in a radiosondeor other probe, which may be operable to measure, e.g., pressure,altitude, geographical position (latitude and longitude), temperature,relative humidity, and/or wind speed and/or wind direction, among otherinformation.

As noted, balloon 300 includes an ultra-bright LED system 320 forfree-space optical communication with other balloons. As such, opticalcommunication system 316 may be configured to transmit a free-spaceoptical signal by modulating the ultra-bright LED system 320. Theoptical communication system 316 may be implemented with mechanicalsystems and/or with hardware, firmware, and/or software. Generally, themanner in which an optical communication system is implemented may vary,depending upon the particular application. The optical communicationsystem 316 and other associated components are described in furtherdetail below.

In a further aspect, balloon 300 may be configured for altitude control.For instance, balloon 300 may include a variable buoyancy system, whichis configured to change the altitude of the balloon 300 by adjusting thevolume and/or density of the gas in the balloon 300. A variable buoyancysystem may take various forms, and may generally be any system that canchange the volume and/or density of gas in the envelope 302.

In an example embodiment, a variable buoyancy system may include abladder 310 that is located inside of envelope 302. The bladder 310could be an elastic chamber configured to hold liquid and/or gas. Thebuoyancy of the balloon 300 may therefore be adjusted by changing thedensity and/or volume of the gas in bladder 310. To change the densityin bladder 310, balloon 300 may be configured with systems and/ormechanisms for heating and/or cooling the gas in bladder 310. Further,to change the volume, balloon 300 may include pumps or other featuresfor adding gas to and/or removing gas from bladder 310. Additionally oralternatively, to change the volume of bladder 310, balloon 300 mayinclude release valves or other features that are controllable to allowgas to escape from bladder 310.

In an example embodiment, the envelope 302 could be filled with helium,hydrogen or other lighter-than-air material. The envelope 302 could thushave an associated upward buoyancy force. In such an embodiment, air inthe bladder 310 could be considered a ballast tank that may have anassociated downward ballast force. In another example embodiment, theamount of air in the bladder 310 could be changed by pumping air (e.g.,with an air compressor) into and out of the bladder 310. By adjustingthe amount of air in the bladder 310, the ballast force may becontrolled. In some embodiments, the ballast force may be used, in part,to counteract the buoyancy force and/or to provide altitude stability.

In another embodiment, a portion of the envelope 302 could be a firstcolor (e.g., black) and/or a first material from the rest of envelope302, which may have a second color (e.g., white) and/or a secondmaterial. For instance, the first color and/or first material could beconfigured to absorb a relatively larger amount of solar energy than thesecond color and/or second material. Thus, rotating the balloon suchthat the first material is facing the sun may act to heat the envelope302 as well as the gas inside the envelope 302. In this way, thebuoyancy force of the envelope 302 may increase. By rotating the balloonsuch that the second material is facing the sun, the temperature of gasinside the envelope 302 may decrease. Accordingly, the buoyancy forcemay decrease. In this manner, the buoyancy force of the balloon could beadjusted by changing the temperature/volume of gas inside the envelope302 using solar energy. In such embodiments, it is possible that abladder 310 may not be a necessary element of balloon 300. Thus, variouscontemplated embodiments, altitude control of balloon 300 could beachieved, at least in part, by adjusting the rotation of the balloonwith respect to the sun.

Further, a balloon 306 may include a navigation system (not shown). Thenavigation system may implement station-keeping functions to maintainposition within and/or move to a position in accordance with a desiredtopology. In particular, the navigation system may use altitudinal winddata to determine altitudinal adjustments that result in the windcarrying the balloon in a desired direction and/or to a desiredlocation. The altitude-control system may then make adjustments to thedensity of the balloon chamber in order to effectuate the determinedaltitudinal adjustments and cause the balloon to move laterally to thedesired direction and/or to the desired location. Alternatively, thealtitudinal adjustments may be computed by a ground-based orsatellite-based control system and communicated to the high-altitudeballoon. In other embodiments, specific balloons in a heterogeneousballoon network may be configured to compute altitudinal adjustments forother balloons and transmit the adjustment commands to those otherballoons.

As shown, the balloon 300 also includes a cut-down system 308. Thecut-down system 308 may be activated to separate the payload 306 fromthe rest of balloon 300. The cut-down system 308 could include at leasta connector, such as a balloon cord, connecting the payload 306 to theenvelope 302 and a means for severing the connector (e.g., a shearingmechanism or an explosive bolt). In an example embodiment, the ballooncord, which may be nylon, is wrapped with a nichrome wire. A currentcould be passed through the nichrome wire to heat it and melt the cord,cutting the payload 306 away from the envelope 302.

The cut-down functionality may be utilized anytime the payload needs tobe accessed on the ground, such as when it is time to remove balloon 300from a balloon network, when maintenance is due on systems withinpayload 306, and/or when power supply 326 needs to be recharged orreplaced.

In an alternative arrangement, a balloon may not include a cut-downsystem. In such an arrangement, the navigation system may be operable tonavigate the balloon to a landing location, in the event the balloonneeds to be removed from the network and/or accessed on the ground.Further, it is possible that a balloon may be self-sustaining, such thatit does not need to be accessed on the ground. In other embodiments,in-flight balloons may be serviced by specific service balloons oranother type of aerostat or aircraft.

In a further aspect, balloon 300 includes a gas-flow system, which maybe used for altitude control. In the illustrated example, the gas-flowsystem includes a high-pressure storage chamber 342, a gas-flow tube350, and a pump 348, which may be used to pump gas out of the envelope302, through the gas-flow tube 350, and into the high-pressure storagechamber 342. As such, balloon 300 may be configured to decrease itsaltitude by pumping gas out of envelope 302 and into high-pressurestorage chamber 342. Further, balloon 300 may be configured to move gasinto the envelope and increase its altitude by opening a valve 352 atthe end of gas-flow tube 350, and allowing lighter-than-air gas fromhigh-pressure storage chamber 342 to flow into envelope 302.

Note that the high-pressure storage chamber 342, in an example balloon,may be constructed such that its volume does not change due to, e.g.,the high forces and/or torques resulting from gas that is compressedwithin the chamber. In an example embodiment, the high-pressure storagechamber 342 may be made of a material with a high tensile-strength toweight ratio, such as titanium or a composite made of spun carbon fiberand epoxy. However, high-pressure storage chamber 342 may be made ofother materials or combinations of materials, without departing from thescope of the invention.

In a further aspect, balloon 300 may be configured to generate powerfrom gas flow out of high-pressure storage chamber 342 and into envelope302. For example, a turbine (not shown) may be fitted in the path of thegas flow (e.g., at the end of gas-flow tube 350). The turbine may be agas turbine generator, or may take other forms. Such a turbine maygenerate power when gas flows from high-pressure storage chamber 342 toenvelope 302. The generated power may be immediately used to operate theballoon and/or may be used to recharge the balloon's battery.

In a further aspect, a turbine, such as a gas turbine generator, mayalso be configured to operate “in reverse” in order to pump gas into andpressurize the high-pressure storage chamber 342. In such an embodiment,pump 348 may be unnecessary. However, an embodiment with a turbine couldalso include a pump.

In some embodiments, pump 348 may be a positive displacement pump, whichis operable to pump gas out of the envelope 302 and into high-pressurestorage chamber 342. Further, a positive-displacement pump may beoperable in reverse to function as a generator.

Further, in the illustrated example, the gas-flow system includes avalve 346, which is configured to adjust the gas-flow path betweenenvelope 302, high-pressure storage chamber 342, and fuel cell 344. Inparticular, valve 346 may adjust the gas-flow path such that gas canflow between high-pressure storage chamber 342 and envelope 302, andshut off the path to fuel cell 344. Alternatively, valve 346 may shutoff the path high-pressure storage chamber 342, and create a gas-flowpath such that gas can flow between fuel cell 344 and envelope 302.

Balloon 300 may be configured to operate fuel cell 344 in order toproduce power via the chemical reaction of hydrogen and oxygen toproduce water, and to operate fuel cell 344 in reverse so as to createhydrogen and oxygen from water. Accordingly, to increase its altitude,balloon 300 may run fuel cell 344 in reverse so as to generate gas(e.g., hydrogen gas), which can then be moved into the envelope toincrease buoyancy. Specifically, balloon may increase its altitude byrunning fuel cell 344 in reverse, adjusting valve 346 and valve 352 suchthat hydrogen gas produced by fuel cell 344 can flow from fuel cell 344,through gas-flow tube 350, and into envelope 302.

To run fuel cell 344 “in reverse,” balloon 300 may utilize anelectrolysis mechanism in order to separate water molecules. Forexample, a balloon may be configured to use a photocatalytic watersplitting technique to produce hydrogen and oxygen from water. Othertechniques for electrolysis are also possible.

Further, balloon 300 may be configured to separate the oxygen andhydrogen produced via electrolysis. To do so, the fuel cell 344 and/oranother balloon component may include an anode and cathode that attractthe positively and negatively charged O− and H− ions, and separate thetwo gases. Once the gases are separated, the hydrogen may be directedinto the envelope. Additionally or alternatively, the hydrogen and/oroxygen may be moved into the high-pressure storage chamber.

Further, to decrease its altitude, balloon 300 may use pump 348 to pumpgas from envelope 302 to the fuel cell 344, so that the hydrogen gas canbe consumed in the fuel cell's chemical reaction to produce power (e.g.,the chemical reaction of hydrogen and oxygen to create water). Byconsuming the hydrogen gas the buoyancy of the balloon may be reduced,which in turn may decrease the altitude of the balloon.

It should be understood that variations on the illustrated high-pressurestorage chamber are possible. For example, the high-pressure storagechamber may take on various sizes and/or shapes, and be constructed fromvarious materials, depending upon the implementation. Further, whilehigh-pressure storage chamber 342 is shown as part of payload 306,high-pressure storage chamber could also be located inside of envelope302. Yet further, a balloon could implement multiple high-pressurestorage chambers. Other variations on the illustrated high-pressurestorage chamber 342 are also possible.

It should also be understood that variations on the illustrated air-flowtube 350 are possible. Specifically, any configuration that facilitatesmovement of gas between the high-pressure storage chamber and theenvelope is possible.

Yet further, it should be understood that a balloon and/or componentsthereof may vary from the illustrated balloon 300. For example, some orall of the components of balloon 300 may be omitted. Components ofballoon 300 could also be combined. Further, a balloon may includeadditional components in addition or in the alternative to theillustrated components of balloon 300. Other variations are alsopossible.

3. BALLOON NETWORK WITH OPTICAL AND RF LINKS BETWEEN BALLOONS

In some embodiments, a high-altitude-balloon network may includesuper-node balloons, which communicate with one another via opticallinks, as well as sub-node balloons, which communicate with super-nodeballoons via RF links. Generally, the optical links between super-nodeballoons may be configured to have more bandwidth than the RF linksbetween super-node and sub-node balloons. As such, the super-nodeballoons may function as the backbone of the balloon network, while thesub-nodes may provide sub-networks providing access to the balloonnetwork and/or connecting the balloon network to other networks.

FIG. 4 is a simplified diagram illustrating a balloon network thatincludes super-nodes and sub-nodes, according to an example embodiment.More specifically, FIG. 4 illustrates a portion of a balloon network 400that includes super-node balloons 410A to 410C (which may also bereferred to as “super-nodes”) and sub-node balloons 420 (which may alsobe referred to as “sub-nodes”).

Each super-node balloon 410A to 410C may include a free-space opticalcommunication system that is operable for packet-data communication withother super-node balloons. As such, super-nodes may communicate with oneanother over optical links. For example, in the illustrated embodiment,super-node 410A and super-node 401B may communicate with one anotherover optical link 402, and super-node 410A and super-node 401C maycommunicate with one another over optical link 404.

Each of the sub-node balloons 420 may include a radio-frequency (RF)communication system that is operable for packet-data communication overone or more RF air interfaces. Accordingly, each super-node balloon 410Ato 410C may include an RF communication system that is operable to routepacket data to one or more nearby sub-node balloons 420. When a sub-node420 receives packet data from a super-node 410, the sub-node 420 may useits RF communication system to route the packet data to a ground-basedstation 430 via an RF air interface.

As noted above, the super-nodes 410A to 410C may be configured for bothlonger-range optical communication with other super-nodes andshorter-range RF communications with nearby sub-nodes 420. For example,super-nodes 410A to 410C may use using high-power or ultra-bright LEDsto transmit optical signals over optical links 402, 404, which mayextend for as much as 100 miles, or possibly more. Configured as such,the super-nodes 410A to 410C may be capable of optical communications atspeeds of 10 to 50 GB/sec or more.

A larger number of balloons may be configured as sub-nodes, which maycommunicate with ground-based Internet nodes at speeds on the order ofapproximately 10 MB/sec. Configured as such, the sub-nodes 420 may beconfigured to connect the super-nodes 410 to other networks and/or toclient devices.

Note that the data speeds and link distances described in the aboveexample and elsewhere herein are provided for illustrative purposes andshould not be considered limiting; other data speeds and link distancesare possible.

In some embodiments, the super-nodes 410A to 410C may function as a corenetwork, while the sub-nodes 420 function as one or more access networksto the core network. In such an embodiment, some or all of the sub-nodes420 may also function as gateways to the balloon network 400.Additionally or alternatively, some or all of ground-based stations 430may function as gateways to the balloon network 400.

4. EXAMPLE BALLONET FOR USE WITH A HIGH-ALTITUDE BALLOON

FIG. 5 is a simplified diagram 500 illustrating a ballonet 510 for useinside of a high-altitude balloon 520, according to an exampleembodiment.

The balloon 520 may take the same form as or be similar in form to theballoon 300 of FIG. 3, in some example embodiments. The balloon 520 maycomprise an envelope 522 and may take various forms, which may becurrently well-known or yet to be developed. For instance, the envelope522 may be made of a highly-flexible latex material or may be made of arubber material such as chloroprene. In one example embodiment, theenvelope and/or skirt could be made of metalized Mylar or BoPet. Othermaterials are also possible. Further, the shape and size of the envelope522 may vary depending upon the particular implementation. The envelope522 is shown to have a generally rounded shape; and more specifically, aspheroid shape having a polar axis shorter than the diameter of theequatorial circle whose plane bisects it. Additionally, the envelope 522may be filled with various different types of gases, such as heliumand/or hydrogen. Other types of gases are possible as well. Moreover,the balloon 520 may be implemented into a balloon network such as theballoon networks of FIGS. 1-2 and 4.

The ballonet 510 may comprise an inflatable bladder within the balloonenvelope 522, and may serve to provide altitude control inside theballoon. The ballonet 510 may comprise a flexible material, may beconfigured to inflate by insertion of liquid and/or gas, and may holdsuch liquid and/or gas. In some example embodiments described herein,the ballonet 510 is designed to comprise about 30% of the volume of theballoon envelope 522. However, other volume percents within the range of20-50% may also be envisioned. The ballonet 510 may not need to have anability to maintain any internal pressure of its own.

The buoyancy of the balloon 500 may be adjusted by changing the densityand/or volume of the gas in ballonet 510. To change the density inballonet 510, balloon 500 may be configured with systems and/ormechanisms for heating and/or cooling the gas in ballonet 510. Further,to change the volume, balloon 500 may include pumps or other featuresfor adding gas to and/or removing gas from ballonet 510. Additionally oralternatively, to change the volume of ballonet 510, balloon 500 mayinclude release valves or other features that are controllable to allowgas to escape from ballonet 510.

In an example embodiment, the balloon 500 interior could be filled withhelium, hydrogen, or other lighter-than-air material. The balloon 500could thus have an associated upward buoyancy force. In such anembodiment, air in the ballonet 510 could be considered a ballast tankthat may have an associated downward ballast force. In another exampleembodiment, the amount of air in the ballonet 510 could be changed bypumping air (e.g., with an air compressor) into and out of the ballonet510. By adjusting the amount of air in the ballonet 510, the ballastforce may be controlled. In some embodiments, the ballast force may beused, in part, to counteract the buoyancy force and/or to providealtitude stability.

The ballonet 510 is shown to be a spheroid or ellipsoid, comprising agenerally oblate shape. The shape of the ballonet may also be describedas pumpkin-shaped or round with flattened poles. The ballonet 510 maycomprise a top pole 512, a bottom pole 514, and an equator shown bydashed line 516.

The shape of the ballonet 510 may be the same as or similar in shape tothe envelope 522, which may serve to improve the stability of theballonet 510 as the ballonet fills with or is filled with liquid/air, oris cooled or heated. As the ballonet 510 inflates, the shape of theballonet 510 (e.g., the flattened bottom pole 514 and curved surfaceextending from the bottom pole 514 toward the top pole 512) may form thesame shape or be similar in shape to the interior surface of theenvelope 522. The exterior surface of the ballonet 510 conforming to theinterior surface of the envelope 522 may aid in the ballonet 510righting itself during the filling process. Additionally, the shapeitself (of flattened poles on a spheroid) may aid in the ballonet 510righting itself during the filling process. The ballonet 510 is thusless likely to fill only to one side, which would destabilize theballonet 510 and the balloon 520. Because the ballonet 510 naturallywants to right itself within the envelope 522, additional stabilizingmeans may not be necessary and the ballonet may only need to be attachedto the bottom of the envelope 522. Having only one attachment pointprovides for easier attachment of the ballonet 510 within the envelope522.

The bottom pole 514 of the ballonet 510 may comprise a hole (shown inFIG. 7) to allow for the insertion of liquid and/or gas. The hole maycomprise a number of sizes. In some example embodiments, the size of thehole may comprise a diameter of about 12 inches. Other diameter holesmay be envisioned. Larger hole sizes allow for high flow rates andfaster altitude change.

The shape of the ballonet 510 allows for the ballonet 510 to be foldedalong the equator 516 and inserted in the folded position within theballoon envelope 522 before completing the final seam of the balloon522. This manner of folding and insertion advantageously provides forless overall handling of the balloon 520 during the insertion process.In some example embodiments, the folding and insertion process mayautomated and may be carried out via a control system comprising programinstructions stored on a non-transitory computer readable medium. Thefolding and insertion process may comprise part of an automated buildingprocess of the balloon 520.

5. ILLUSTRATIVE METHODS

FIG. 6 is a flow chart of a method, according to an example embodiment.Example methods, such as method 600 of FIG. 6, may be carried out by acontrol system. A control system may take the form of programinstructions stored on a non-transitory computer readable medium (e.g.,a memory) and a processor that executes the instructions. However, acontrol system may take other forms including software, hardware, and/orfirmware. The control system may execute instructions to an automatedassembly manufacturing line, in some example embodiments.

The method 600 is a method to provide a ballonet for a balloon, such asthe ballonet 510 of FIG. 5. As shown by block 610, method 600 involvesproviding a plurality of sheets, wherein each sheet comprises aperimeter. Each of the plurality of sheets may comprise a plastic filmwhich may be coated with a barrier. Example barriers may comprisepolyamide, ethylene vinyl alcohol (EVOH), and metallized aluminium, forexample. The plurality of sheets may comprise pre-cut sheets or may becut from one or more elongated pieces of the material. The sheets may becut to form a circular shape, an octagon shape, or a number of othergeometric shapes. The size of the sheets may be variable to provide fordifferent sizes of ballonets. Two such example sheets are described andshown with reference to FIG. 7 below.

Then at block 620, method 600 involves seaming two of the plurality ofsheets together to form an oblate-shaped ballonet. Two sheets of thesame size may be placed on top of one another and aligned such that theedges of each sheet are aligned. The sheets may then be seamed togetheralong the perimeters of each sheet. When inflated, the formed shape willcomprise an oblate spheroid having a polar axis shorter than thediameter of the equatorial circle whose plane bisects it. For example,the distance between two poles is less than the equatorial distance ofthe spheroid.

At block 630, method 600 involves forming a hole through one of thesheets. The sheet with the hole formed therethrough will comprise thebottom sheet and will be attached to the inside of a balloon envelope asdescribed in FIG. 5.

At block 640, method 600 involves inserting the ballonet into a balloon.The ballonet may be folded prior to insertion into the balloon. In someexample embodiments, the ballonet may be folded along the equator of itsbody as described in FIG. 5.

The method 600 may further include sealing the ballonet with a gasket ata base of a balloon. In some example embodiments, the gasket is aconformable gasket and the seal is a pinch seal. In another embodiment,the method 600 may further include heat sealing the ballonet to theenvelope and burying the seal in the base fitting, which is where theballonet is mounted to the base of the envelope and the air intake islocated. The heat sealing method may provide for a stronger barrier ofthe base fitting.

FIG. 7 is a simplified diagram illustrating sheets to manufacture aballonet, according to an example embodiment. The sheets may be used inthe method 600 to manufacture a ballonet such as the ballonet 510 ofFIG. 5. In FIG. 7, two example sheets are used in accordance with themethod of FIG. 6 to manufacture a ballonet that is insertable for usewithin a balloon envelope. A first sheet 710 and a second sheet 720 areprovided. A perimeter 730 is provided for both the first sheet 710 andthe second sheet 720. The first sheet 710 and the second sheet 720 maybe attached to each other at each perimeter 730, as described withrespect to block 620 in method 600. A hole 740 may be formed through thesecond sheet 720. The sheets 710, 720 then extend in opposite directionsas the ballonet inflates to create the oblate spheroid shape.

6. CONCLUSION

The above detailed description describes various features and functionsof the disclosed systems, devices, and methods with reference to theaccompanying figures. While various aspects and embodiments have beendisclosed herein, other aspects and embodiments will be apparent tothose skilled in the art. The various aspects and embodiments disclosedherein are for purposes of illustration and are not intended to belimiting, with the true scope and spirit being indicated by thefollowing claims.

What is claimed is:
 1. An inflatable bladder comprising: a spheroid bodycomprising an equator, a top pole, a bottom pole, and an axis crossingthrough the top pole and the bottom pole perpendicular to the equator;wherein a distance around the equator is greater than a distance aroundthe axis, creating an oblate spheroid shape when fully inflated; whereinthe inflatable bladder is insertable into an envelope of a balloon;wherein the envelope has a corresponding oblate spheroid shape, andwherein when inflated, at least a portion of an outer surface of theinflatable bladder conforms to an inner surface of the envelope.
 2. Theinflatable bladder of claim 1, wherein the envelope is a superpressureenvelope.
 3. The inflatable bladder of claim 1, wherein the balloon is ahigh-altitude balloon that is deployable in the stratosphere.
 4. Theinflatable bladder of claim 1, wherein the inflatable bladder is aballonet configured to hold liquid or gas.
 5. The inflatable bladder ofclaim 4, wherein the ballonet is made from a plastic film coated with abarrier.
 6. The inflatable bladder of claim 1, wherein the ballonet isfoldable for insertion into the envelope.
 7. The inflatable bladder ofclaim 1, wherein the spheroid body is an oblate spheroid.
 8. A variablebuoyancy system comprising: a balloon comprising an envelope, whereinthe envelope comprises an interior that contains a liquid or gas; aballonet within the envelope interior, the ballonet comprising: anoblate spheroid body comprising an equator, a top pole, a bottom pole,and an axis crossing through the top pole and the bottom poleperpendicular to the equator; wherein a distance around the equator isgreater than a distance around the axis when fully inflated; wherein theenvelope has a corresponding oblate spheroid shape, and wherein wheninflated, at least a portion of an outer surface of the ballonetconforms to an inner surface of the envelope.
 9. The variable buoyancysystem of claim 8, wherein the envelope is a superpressure envelope. 10.The variable buoyancy system of claim 8, wherein the balloon is ahigh-altitude balloon that is deployable in the stratosphere.
 11. Thevariable buoyancy system of claim 8, wherein the ballonet comprises afoldable and inflatable bladder configured to hold liquid or gas. 12.The variable buoyancy system of claim 11, wherein the ballonet comprisesa plastic film coated with a barrier.